A printing plate is ordinarily prepared by exposing to light a presensitized planographic printing plate and developing the exposed plate with liquid developer. This process, however, produces waste liquid developer which must be discarded, resulting in environmental problems.
Recently, a method (dry plate-making process) for making a printing plate without employing liquid developer has been studied, and various methods have been proposed for the dry plate-making process,
For example, there is proposed a method of preparing a planographic printing plate according to a transfer method, however, this method has a problem of producing image defects. Further, there is proposed a method preparing a planographic printing plate according to an ablation method, however, this method has a problem in that the ablated scatters and soils the surroundings, and further a specific development machine is required for forming an image in a closed system.
To the contrary, physical property change type planographic printing plate material is preferable which can form an image employing oleophile-hydrophile property change, since this material makes it possible to prepare a planographic printing plate without liquid development.
Various physical property change type planographic printing plate materials have been proposed. For example, in Japanese Patent O.P.I. Publication No. 62-164049 is disclosed a planographic printing plate material comprising a hydrophilic support, and provided thereon, a recording layer containing a block isocyanate and an active hydrogen-containing resin capable of reacting with an isocyanate, wherein the support or the recording layer contains a light-heat converting compound. This technique provides improved durability at exposed portions, since isocyanate produced by heat application reacts with the resin, however, this comprises a developing step of dissolving unexposed portions with a liquid developer. When a planographic printing plate prepared from this material without liquid development after exposure is used, it produces dissolution of non-exposed portions and stains on dampening rollers during printing, resulting in adverse effects on the printing properties.
A method employing capsules was proposed, but the method has a problem of resolving power resulting from the capsule size.
In Japanese Patent O.P.I. Publication No. 51-63704 is disclosed a method of preparing a planographic printing plate, imagewise exposing to laser a planographic printing plate material without any further treatment after exposure, which has, on a support, a hydrophilic layer containing dyes and a non-light sensitive compound such as PVP, PVA, casein, dextrin, gum arabic, HEC, PEG, polyacrylic acid, or PVPA. However, this method is not necessary satisfactory, since it has problems of low sensitivity and high noise.
In U.S. Pat. No. 4,081,572 is disclosed a physical property change type planographic printing plate material comprising a support, and provided thereon, a hydrophilic layer containing a specific hydrophilic polymer, in which the hydrophilic layer is made hydrophobic by imagewise energy exposure. In this case, change from the hydrophilic to hydrophobic layer at image portions is realized by decarboxylation of the hydrophilic polymer, and therefore, strength of the image portions and the non-image portions is not sufficient, resulting in lowering of printing durability.
In view of the above, the present invention has been made. The present invention provides a planographic printing plate prepared by a dry plate-making process, and provides a planographic printing plate material which is inexpensive, and gives improved sensitivity, S/N, and strength at image portions and non-image portions, and high resolving power.